/**
 * RED metrics for nifra as an opt-in `.use(metrics())` plugin, exposed in Prometheus text format at
 * `/metrics`. Dependency-free and in-process: an atomic counter/gauge/histogram registry with a
 * Prometheus renderer, plus automatic per-request rate/errors/duration series labeled by the matched
 * route TEMPLATE (not the raw path, so `/users/:id` is one series, not one per id).
 *
 *   import { metrics } from "@nifrajs/otel/metrics"
 *   const app = server().use(metrics()).get("/users/:id", handler)
 *   // GET /metrics → nifra_http_requests_total{method="GET",route="/users/:id",status="200"} 5 …
 *
 * `c` is not touched; apps that want custom app metrics create their own registry and pass it in
 * (`metrics({ registry })`), then register series on it - they render at the same `/metrics`.
 */
import { type IdentityPlugin } from "@nifrajs/core/server";
type Labels = Readonly<Record<string, string>>;
/** A monotonically increasing counter (requests, errors). */
export declare class Counter {
    readonly name: string;
    readonly help: string;
    private readonly series;
    constructor(name: string, help: string);
    inc(labels?: Labels, by?: number): void;
    render(): string;
}
/** A value that can go up and down (in-flight requests, queue depth). */
export declare class Gauge {
    readonly name: string;
    readonly help: string;
    private readonly series;
    constructor(name: string, help: string);
    private at;
    inc(labels?: Labels, by?: number): void;
    dec(labels?: Labels, by?: number): void;
    set(labels: Labels, value: number): void;
    render(): string;
}
/** Latency-style distribution over fixed buckets (seconds). Renders Prometheus cumulative buckets. */
export declare class Histogram {
    readonly name: string;
    readonly help: string;
    private readonly series;
    private readonly buckets;
    constructor(name: string, help: string, buckets: readonly number[]);
    observe(value: number, labels?: Labels): void;
    render(): string;
}
/** A collection of metrics that renders one Prometheus exposition document. */
export declare class MetricsRegistry {
    private readonly counters;
    private readonly gauges;
    private readonly histograms;
    counter(name: string, help?: string): Counter;
    gauge(name: string, help?: string): Gauge;
    histogram(name: string, buckets: readonly number[], help?: string): Histogram;
    /** The Prometheus text exposition of every registered series. */
    render(): string;
}
/** Create a standalone registry to register custom app metrics on, shared into `metrics({ registry })`. */
export declare function createMetricsRegistry(): MetricsRegistry;
export interface MetricsOptions {
    /** Where to expose the Prometheus text. Default `/metrics`. This route is excluded from the metrics. */
    readonly path?: string;
    /** Reuse a registry (so custom app metrics render alongside the RED series). Default: a fresh one. */
    readonly registry?: MetricsRegistry;
    /** Histogram buckets in SECONDS for request duration. Default OpenTelemetry latency buckets. */
    readonly buckets?: readonly number[];
}
/**
 * Enable RED metrics + a `/metrics` Prometheus endpoint. Records `nifra_http_requests_total`,
 * `nifra_http_request_duration_seconds`, and `nifra_http_requests_in_flight`, labeled by method,
 * matched route template, and status. Apply once (named-plugin dedupe).
 */
export declare function metrics(options?: MetricsOptions): IdentityPlugin;
export {};
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